using System;

using System.Collections.Generic;

using System.Data;

using System.Data.SqlClient;

using System.Linq;

public class Program

{

    public class A

    {

        public int B { get; set; }

    }

​

    public static void Main()

    {  

        var arr1 = new List<A>()

        {

            new A() {B = 10},

            new A() {B = 20}

        };

        var arr2 = new List<A>()

        {

            new A() {B = 10},

            new A() {B = 20}

        };

        arr1.Select(x=>{x.B=0;return x;}).ToList();

        arr2.Select(x=>{x.B=0;return x;});

        Console.WriteLine("arr1 <===============>");

        foreach(var item in arr1){

            Console.WriteLine(item.B);

        }

        Console.WriteLine("arr2 <===============>");

        foreach(var item in arr2){

            Console.WriteLine(item.B);

        }

    }

}